The invention relates to an apparatus for damping courses of motion such as those which occur in vehicle suspension systems. In a known apparatus of this type (U.S. Pat. No. 3,807,678), in a suspension system for two masses, one of which may be one or more wheels of a vehicle and the other of which may be the vehicle body, a standard passive compression spring is disposed between the two masses; this is known as a passive isolator, and a so- called active damper is connected parallel to it. This damper, which has a piston sliding in a cylinder and dividing the cylinder into two working chambers, is considered to be active because of what may be called an active intervention into the damping characteristics, that is, into the volumetric displacement of the pressure medium, is made in the respective working halves of the damper by means of a control function. To this end, the two working chambers are connected crosswise and parallel to each other via opposed valves allowing a flow of pressure medium in only one direction; the amount of pressure medium then allowed to pass through these valves then also becomes "active" by appropriate control of the valves by means of suitably prepared sensor signals. Because in this known suspension system, the spring itself is entirely passive, but the damper is conceived of as being active in terms of its properties, the overall system in this patent is called a semi-active system. However, this term is not semantically related to the dampers of the present invention, which without reference to suspension systems not taken into account are themselves designated as so-called semi-active dampers, for reasons to be explained hereinafter.
It is also known, in wheel suspensions in vehicles, to provide so-called active damping means (see the article, "Active Damping in Road Vehicle Suspension Systems", published in the periodical, Vehicle System Dynamics, 12 (1983), pages 291-316). This publication is referred to also because it includes basic concepts, in theoretically detailed form, applicable in particular to active damping properties.